JP2004279532A - Spread plate and light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spread plate for relieving a "lamp image" and prevention of lowering of the luminance in a light-emitting device with a lamp arranged behind the spread plate. <P>SOLUTION: The spread plate comprises a transparent substrate 20, a high base layer 21 for transmittance regulation provided on one face of the transparent substrate 20, and a spread bead layer 22 for luminance improvement provided on the other face of the transparent substrate 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a diffusion plate and a light emitting device.
[0002]
[Prior art]
In recent years, a direct backlight type light emitting device has been increasingly used as a large flat light emitting device exceeding 15 inches. An example of such a light emitting device is described in Patent Document 1, and its basic configuration is provided with a lamp behind a diffusion plate for diffusing light.
Conventionally, as a diffusion plate manufactured and sold, a milky white plate in which a diffusion agent is mixed with a resin plate such as acrylic or polycarbonate is generally used.
[0003]
[Patent Document 1]
JP-A-8-202298
[Problems to be solved by the invention]
Generally, in a light emitting device in which a lamp is arranged behind a diffusion plate, a problem of generating a lamp image occurs. The lamp image is represented by the shape and arrangement of the lamp as the intensity of light on the diffusion plate, and the presence of the lamp image impairs the light emission quality of the light emitting device.
Here, according to the knowledge of the inventors, the occurrence of a lamp image is closely related to the light transmittance of the diffusion plate. That is, when the transmittance is high, the lamp image is easily seen, and when the transmittance is low, the lamp image is moderated.
Therefore, in order to alleviate the lamp image, the transmittance of the diffusion plate may be reduced. However, in the case of a diffusing plate mixed with a diffusing agent, if the transmittance of the diffusing plate is reduced, the amount of the diffusing agent increases, light is absorbed inside the diffusing plate, light loss is increased, and brightness is reduced. . Further, when the amount of the diffusing agent is large, there is a problem that blue light is absorbed inside the diffusing plate and the light becomes yellow.
Therefore, an object of the present invention is to prevent a decrease in luminance due to a decrease in transmittance.
[0005]
[Means for Solving the Problems]
The present invention is configured to include a high-haze layer for transmittance adjustment provided on one surface of the transparent substrate, and a light-diffusing layer provided on the other surface of the transparent substrate. Is a diffusion plate. The high haze layer preferably has a haze value of 80% or more.
Further, the light emitting device according to the present invention is a transparent substrate, a lamp disposed behind the transparent substrate, a high haze layer disposed on a surface of the transparent substrate on the lamp side, and the lamp side of the transparent substrate. And a light-diffusing layer disposed on the opposite surface.
According to the present invention, there is no light loss in the transparent substrate, and light is dispersed and reflected by the high haze layer to reduce the transmittance. Therefore, even if the transmittance is reduced, a reduction in luminance is prevented. Also, the light coming out of the diffusion layer is condensed, so that the brightness increases.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a basic configuration of a light emitting device 1 used as a Schaukasten for observing an X-ray photographic film. The light emitting device 1 includes a casing 3 having an open surface on which a diffusion plate 2 is installed. 4 are arranged. As the lamp 4, a linear light source, more specifically, a cold cathode fluorescent lamp is used, and a plurality of lamps 4 are arranged in the casing 3 in parallel at a predetermined interval.
[0007]
The bottom surface 3a and / or the side surface 3b inside the casing 3 is a reflecting surface for reflecting light from the lamp 4. The reflecting surface can be constituted by white painting of the casing 3 or laying of a white sheet. The reflection surface is preferably a diffuse reflection surface, and preferably has a reflectance of 80% or more, more preferably 90% or more, and still more preferably 95% or more.
[0008]
The light from the lamp 4 enters from one surface 2a of the diffuser plate 2 directly or via reflection by the reflection surfaces 3a and 3b, and exits from the other surface 2b on the opposite side. That is, the surface 2a on the lamp 4 side of the diffusion plate 2 is a light incident surface, and the surface 2b on the opposite side is a light emitting surface (light emitting surface).
[0009]
FIG. 2 is an enlarged cross-sectional view of the diffusion plate 2. The diffusion plate 2 includes a transparent substrate 20 having a transparent resin plate (acrylic plate, polycarbonate plate, or the like) or a transparent glass plate as a substrate. A high haze layer 21 is formed on the lamp 4 side of the substrate 20, and a diffusion bead layer (diffusion layer) 22 is formed on the opposite side.
When the transparent substrate 20 is too thin, it is difficult to alleviate the lamp image, and in order to secure rigidity as a diffusion plate, it is preferably 0.5 mm or more. Is preferred. More specifically, a thickness of about 2 mm is preferable.
[0010]
In the diffusion plate 2, the relaxation of the lamp image is mainly performed by the high haze layer 21. The high haze layer 21 is for lowering the transmittance in the normal direction of the diffusion plate, and reflects the light emitted from the lamp 4 toward the lamp 4 to reduce the light transmittance of the diffusion plate 2 to reduce the lamp image. To a certain extent. The high haze layer 21 has a thickness of about 20 μm, and is formed of acrylic beads, silica beads, titanium oxide beads, or a composite thereof. The high haze layer 21 may be organic or inorganic.
[0011]
The haze value of the high haze layer 21 alone is preferably higher, preferably 70% or more, and more preferably 80% or more. The high haze layer 21 reflects light and adjusts light transmittance. In order to surely eliminate the lamp image, the haze value of the entire diffusion plate 2 (haze value of the high haze layer 21 and the diffusion bead layer 22) is preferably 75% or more, more preferably 80%. Above, more preferably 90% or more.
[0012]
The light transmittance of the high haze layer 21 (transmittance when only the high haze layer 21 is applied to the transparent substrate 20 and light is applied from the high haze layer 21 side (see FIG. 3)) is 25% to 68%. %, Particularly preferably about 55%.
The light transmittance of the entire diffusion plate 2 (the transmittance of the high haze layer 21 and the diffusion bead layer 22 combined) is preferably low enough to alleviate the lamp image, specifically, about 70%. Or less, more preferably about 50% or less, even more preferably about 40% or less. Further, the transmittance of the entire diffusion plate 2 is preferably 20% or more, and more preferably 30% or more.
[0013]
Rather than lowering the transmittance over the entire thickness of the milky white diffusion plate as in the related art, the transmittance is reduced by reflection of light on the lamp-side surface 2a, as in the case of the diffusion plate 2, so that the transparent substrate 20 Thus, light loss can be reduced.
That is, if the amount of the diffusing agent (and the light adjusting agent) as an additive is increased to reduce the transmittance, the amount of light absorbed by the diffusing agent and the like increases, and the light loss increases. Since the substrate 20 occupying most of the thickness of the diffusion plate 2 is transparent, light loss inside the diffusion plate 2 is small. Further, when the amount of the diffusing agent is large, blue light is absorbed and the emission color becomes yellowish, but this is prevented in the present embodiment.
The adjustment of the transmittance is performed by the reflection of light on the high haze layer 21. The light diffusely reflected by the high haze layer 21 is re-reflected on the casing reflection surfaces 3a and 3b (although there is some loss), and most of the light finally exits from the diffusion plate 2, so that the entire diffusion plate 2 is emitted. Can be prevented from decreasing.
[0014]
In other words, according to the diffuser plate 2 according to the present embodiment, since the transmittance in the normal direction of the diffuser plate is reduced by the high haze layer 21, light in the normal direction, which causes a lamp image, is reduced. Most of the light from the lamp 4 can be finally emitted from the diffusion plate 2, so that the decrease in luminance is small.
Moreover, light that has undergone double diffuse reflection, that is, diffuse reflection at the high haze layer 21 and diffuse reflection at the reflecting surfaces 3a and 3b (particularly, the reflecting surface 3a) becomes relatively uniform diffused light, thereby suppressing generation of a lamp image. Is done. As described above, in the present embodiment, sufficient diffused light is obtained by the reflection surfaces 3a and 3b on the inner surface of the casing and the high haze layer 21 of the diffuser plate 2, so that even if the substrate 20 is transparent, good light emission quality is obtained. Is obtained.
[0015]
In the high haze layer 21, the light entering the transparent substrate 20 is also diffused. Since the diffused light enters the transparent substrate 20, even if light from the lamp 4 directly enters the diffusion plate 2 in the vertical direction, the light is diffused so as to spread in the diffusion plate surface direction, and the lamp image is blurred. Relaxation due to misalignment of the image is obtained. In order to obtain diffused light, the high haze layer 21 is preferably a bead layer formed by beads as described above.
[0016]
The diffusion bead layer 22 on the light exit surface 2b side of the diffusion plate 2 has transparency and is the same as the diffusion bead layer generally used for a diffusion sheet for increasing luminance. The diffusion bead layer 22 has directivity, and a transparent sheet (a PET sheet having a thickness of 0.1 mm) having a haze value of 70% or more when one side of the diffusion bead is coated with a transparent substrate 20 , A good diffusion bead layer could be formed. Specifically, as the diffusion beads, beads used for a diffusion sheet 100GM2 manufactured by Kimoto Co., Ltd. or a diffusion sheet BS-04 manufactured by Ewa Co., Ltd. are preferable. The thickness of the diffusion bead layer 22 is preferably about 20 μm.
[0017]
In the diffusion bead layer 22, the light (diffused light) that has passed through the transparent substrate 20 is condensed in a direction perpendicular to the diffusion plate 2 to improve the brightness. Further, since the luminance can be obtained even without the optical sheet (diffusion sheet) placed on the diffusion plate 2, the cost can be reduced. Further, the diffusion layer 22 may be an optical sheet such as a diffusion sheet separate from the transparent substrate 20, but in the present embodiment, since the diffusion bead layer 22 is formed on the rigid substrate 20, More resistant to damage than low optical sheets. Therefore, like a light emitting device such as a Schaukasten, a light-emitting signboard, or a lighting box used in a state where the light-emitting surface 2a is exposed to the outside, as a diffusion plate, a hand or an object may contact the light-emitting surface 2a. The diffusion plate 2 of the present embodiment is preferable. Further, in the diffusion plate 2 of the present embodiment, even if there is no optical sheet, uniform light emission quality (relaxation of a lamp image) and high luminance can be obtained by using the diffusion plate 2 alone, so that no optical sheet is used on the light exit surface 2a side. It is suitable as a diffusion plate for a light emitting device.
The diffusion bead layer 22 also diffuses light, which contributes to further alleviation of the lamp image.
[0018]
Further, since the diffusion bead layer 22 is formed on the light emitting surface 2a, fine irregularities are formed on the light emitting surface 2a, and when an optical sheet is laid on the light emitting surface 2a (backlight for a liquid crystal display device), and the like. In this case, it is possible to prevent the optical sheet from adhering to the light exit surface 2a, and this is particularly suitable when a lens sheet or the like having high adhesion is placed as the optical sheet.
[0019]
According to the diffusion plate 2 according to the present embodiment, the light that is going to enter the diffusion plate 2 from the lamp 4 side is reflected by the high haze layer 21 by a predetermined amount, so that the light is diffused by the transparent substrate 20 having a high transmittance. Even if it is formed, the transmittance of the entire diffusion plate 2 is adjusted to be low, and the lamp image is improved. Moreover, since the diffusion plate 2 is mostly formed of the transparent substrate 20, light loss in the diffusion plate 2 is small, and the lamp image can be improved while preventing a decrease in luminance. .
Further, in the high haze layer 21, since light diffusion is performed, there is a positional shift between the light entering from the light incident surface 2a and the light exiting from the light emitting surface 2b. Helps with mitigation. Further, the lamp image is also reduced in the diffusion bead layer 22 by light diffusion.
In the light exit surface 2b, the luminance is improved by increasing the directivity of light. As a whole, the diffuser plate 2 can reduce the light transmittance by reducing the light transmittance, and at the same time, can prevent the luminance decrease. Has been achieved.
[0020]
Note that the present invention is not limited to the above embodiment. For example, the light emitting device of the present invention may be used as a light box for viewing a photographic negative or the like, a light emitting signboard, a backlight of a liquid crystal display device, and the like, in addition to the Schaukasten.
[0021]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, while reducing a transmittance | permeability, a lamp image can be eased and a brightness fall can be prevented even if a transmittance | permeability is reduced.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a direct backlight.
FIG. 2 is an enlarged sectional view of a diffusion plate.
FIG. 3 is a diagram showing a method for measuring the transmittance of a high haze layer.
[Explanation of symbols]
1 backlight (light emitting device)
2 Diffusion plate 20 Transparent substrate 21 High haze layer 22 Diffusion bead layer (diffusion layer)

Claims (3)

A transparent substrate,
A high haze layer for transmittance adjustment provided on one surface of the transparent substrate,
A light-diffusing layer provided on the other surface of the transparent substrate,
A diffusion plate characterized by comprising: 2. The diffusion plate according to claim 1, wherein the high haze layer has a haze value of 80% or more. A transparent substrate,
A lamp disposed behind the transparent substrate,
A high haze layer disposed on the lamp-side surface of the transparent substrate,
A light-condensing diffusion layer disposed on a surface of the transparent substrate opposite to the lamp side.

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